Had a recent situation where an out of office reply created 100,000 tickets...yes...100,000.

I read in the following article for FP 12 that the system can block emails from an address if 5 of the last 15 emails have the same from address. It says to update the MRlocaldefs files and I believe the FP 20.18.02 eliminated that file.

Does anyone know how to have the same sort of functionality in this version?

Go to Administration, Incoming Email (System) then click the Out of Office tab, you should turn that functionality on there. It works 99% of the time, randomly every now and then, it will let one slide through but that is very very rare for us.